1. Field of the Invention
The present invention relates to a small watercraft including a jet pump disposed at a rear portion of a hull constituting a lower portion of the watercraft.
2. Background of the Invention
A known small watercraft includes a jet pump disposed at a rear portion of a hull that constitutes a lower portion of the watercraft. Water is expelled rearwardly from a trailing end of the jet pump to let the watercraft plane (see, for example, FIG. 2 of Japanese Patent Laid-Open No. 2004-98973).
Referring to FIG. 2 of Japanese Patent Laid-Open No. 2004-98973, a small surface boat 10 includes a vessel body 11 (the same reference numeral as that of Japanese Patent Laid-Open No. 2004-98973 have been used herein) and a water jet propeller 17 (hereinafter referred to as “jet pump 17”). The vessel body 11 includes an intake port 29 disposed at a hull bottom 28. The jet pump 17 is disposed at a rear portion of a hull that constitutes a lower portion of the vessel body 11. The intake port 29 is extended up to the jet pump 17. The jet pump 17 is rotated, so that water taken in is expelled rearwardly from the intake port 29.
Rotating an impeller 32 of the jet pump 17 under water generates a pressure difference in areas between a front side and a backside of the impeller 32. Cavitation can then occur in low-pressure regions having a low pressure. The cavitation causes the pressure in the jet pump 17 to fluctuate, resulting in the jet pump 17 vibrating. The vibration is transmitted to the vessel body 11 via a wall portion 30 of a jet pump chamber 16. The vessel body 11 is then vibrated and comfort during planing is impaired.